Before a facsimile image is transmitted from an originating facsimile machine to a terminating facsimile machine, the originating and terminating facsimile machines send messages between the machines to negotiate transmitting and receiving modes for transmitting facsimile data. Such transmitting and receiving modes specify a set of parameters that are agreed upon prior to transmitting facsimile data. These parameters may include a data bit rate, a page size, the number of pixels per line, the number of lines per page, and whether or not any fill characters are added to a line so that the terminating facsimile machine has time to print each line. However, prior to the negotiation of transmitting and receiving modes, a negotiation for call completion occurs between the originating facsimile machine and the terminating facsimile machine. This call completion negotiation may pose a problem in systems having long call setup times. The call setup times may be effected by the number of rings on the terminating facsimile machine before it picks up, switching times related to a PBX switch, switching times related to international calls, and the like. In addition, systems having a variable data transmission time add additional delays on top of those previously mentioned, which in turn may cause the call completion rate between the originating and terminating facsimile machines to be undesirably low.
When an originating facsimile machine and a terminating facsimile machine need to transmit facsimile data, the negotiation for call completion between the originating facsimile machine and the terminating facsimile machine, as well as the negotiation of transmitting and receiving modes, becomes important to the success of sending a facsimile image. An example of a medium having a variable data transmission time is a wireless medium, which may, for example, be used to provide wireless local loop telephone service to businesses and homes. The reason this wireless communications system may be considered a medium having a variable data transmission time is that the wirelessly transmitted data may be influenced by noise or interference from other users, and thus may need to be retransmitted to correct errors. This retransmission takes time and may introduce delay in the overall communications link between the originating and terminating facsimile machines. The Internet or other similar network is another example of a communication medium having a variable data transmission time. Such mediums do not have a low, fixed time of data propagation. Other examples include a medium that allows random quantities of data with variable periods of idle or null characters to be synchronously transmitted.
In a wireless local loop system, telephones, facsimile machines, and other terminal equipment at the customer's site may be connected to a device frequently referred to as a fixed wireless terminal (FWT). The fixed wireless terminal provides basic telephone local loop service through a wireless or radio link. In many service areas, telephone service may be provided wirelessly at a fraction of the cost of traditional wireline infrastructure. Other benefits of wireless local loop systems are rapid deployment time, the ability to cover a large area, high capacity, and lower operating and maintenance costs.
Many wireless local loop systems are implemented with a digital air interface between the fixed wireless terminal and a base station transceiver. This means that signals from a facsimile machine connected to the fixed wireless terminal must be converted from an analog signal to a digital signal before transmission over the air. Similarly, digital signals received from the base transceiver must be converted to analog signals in the fixed wireless terminal before they are sent to a connected facsimile machine. All of these conversions may introduce delay into the system. In addition, the time and number of access probes required to access the call is variable, and may introduce a delay. To further complicate the problem, the originating facsimile machine expects a timely reply from the terminating facsimile machine after dialing is completed on originated calls.
Most facsimile machines include a start connection timer having a predetermined time duration which is activated as soon as dialing is completed on originated calls. This start connection timer will disconnect the call if an HDLC message is not received by the originating facsimile machine from the terminating facsimile machine prior to the expiration of the connection timer. HDLC messages are sent between facsimile machines in accordance with the T.30 procedures for Document Facsimile Transmission in the General Switched Telephone Network specification, which is promulgated by the International Telecommunication Union (ITU). Typically, the connection timer value is based on wireline timing characteristics. As discussed above, wireless calls introduce additional call set-up delays which can result in the connection timer expiring and the call being dropped by the originating facsimile machine prior to the call being completed between the originating and terminating facsimile machines.
While the foregoing discussion relates to a wireless communication link in a wireless local loop communications system, other communications media having either fixed and/or variable data transmission times may have similar problems supporting a facsimile data transmission session. Therefore, there is a need for an improved method and apparatus for preventing an originating facsimile machine from going on-hook prior to call completion due to setup delays.